On a current project, I'm soldering this header on a board: http://www.digikey.com/product-detail/en/BM10B(0.6)-20DP-0.4V(51)/H11951TR-ND/2712174
The header seems great, it's small and low profile, perfect for this application. However, I'm having some serious issues with the soldering due to the very fine 16 mil pitch. My first revision of the board I tried to apply solder paste by hand and I kept getting solder bridges on my boards. I marginally lengthened the pads from the manufacturer's recommendations with the second revision in the hope that the solder would flow out along the pads versus jumping the soldermask between the pads. I also got a stencil to better control the amount of solder paste I applied on each pad. But I'm still getting a lot of bridging!
It's lead free solder, as I'd like the end product to be RoHS compliant.
Any tips on what I could do from a design and execution standpoint to get this right? Do I lenghten the pads more? Should I shrink them? Should I have the stencil holes made smaller? Do I need to change my heating profile?
Help would be appreciated - thanks!
The pads are too small for me to be very accurate when trying to apply the paste by hand, which is why I got the stencil for the second revision. I'd like to reinforce that the center to center distance for these pads is less than half a millimeter, if I had hands that steady, I'd have been a doctor. So I agree with the reasoning, I'm just curious if you have any suggestions on the execution.
On the third revision, I imagine I'll get another stencil - should I make the stencil openings thinner for these pads so that there is less solder and a greater distance between the solder on the pads?
I appreciate your guys' feedback!
Hey Chuck, does the nail polish container have any influence on the liquid flux or is it just a lot easier to dispense? And any recommendation on the type of flux? I've used the no-clean stuff before and it seemed to help a little but I've heard that it's not as effective.
The flux came in a chem type bottle and I would pure it into a nail polish container for use. When hand soldering a QFP or a SMT connector I would apply a tiny bit of solder to the two most opposite pads (just to hold the device in place and lined up with the pads). Then using my "nail polish" wipe a healthy amount of flux clear across all the pins. Then using a small soldering tip heat up each pad barely touching the very end of the components pin and solder each pin. If you get a solder bridge at this point no problem. Once the component is soldered correctly I apply a little more flux clear across all the pins again right on top of all the pins and solder bridges. Then over each bridge or connection with too much solder you can wipe the bridge away running the iron parallel away from the device along the pins. If there is WAY too much solder you can get rid of it with a little copper braid.
As far as the type of flux, I have no idea to be honest. All I know is that I was using normal solder (lead/tin, 80/20 i believe) (I did not care about ROHS) because the lead free solder sucks. The flux was certainly NOT no-clean. I left a mess behind on the PCB (but the device was solder perfectly). I would clean up using a spray can of flux off, a chem wipe, and a short brisel chem brush (that made it spotless). The flux was 10W 30 motor oil consistancy.
I bought it from Techni-Tool, standard, nothing special, probably the most expensive since I worked for the government and money was no object. lol
As far as pad size on the PCB, Solder Mask layer, solder paste stencil, I have some of my own tricks of the trade that help certain problems depending on if the component is a QFP, BGA, or connector, if my board is being machine build by a pick and place robot, if the solder paste if being applied by a wiping action on a stencil or not, etc etc. But normally pad size is determined by lead shape and footprint by the manufacturer. I may alter the footprint slightly if I know I am going to hand solder these devices.
Hope that helps
Hey Chuck, things turned out kinda weird, not what I was expecting. I got a gel like flux from Radio Shack and some of the finest pitch solder I could find to solder it by hand instead of in the reflow oven. Instead of experimenting on the main board, I tried it on a mating board that was a lot smaller and cheaper if I killed it. The first attempt was semi-successful in execution but hugely successful in learning. So, I'll say what I did on the second one I tried.
After I got the piece in position, I held it perfectly still with some tweezers. Then, using some of that fine solder I bought, I dipped it in super glue and wiped it where the board and connector meet . I let it dry. The reason I didn't go straight from the super glue bottle is that in my first attempt, it wicked out and covered about a third of the connector, not good. I wiped the flux across the leads with a q-tip which was functional but a bad idea to use a q-tip. I need a fine brush, it was hard to apply a reasonable amount and I was plucking cotton strands out of the connector. The most interesting part comes next. I then didn't use the solder. The tinning on the pads was sufficient to connect the leads. I simply touched my fine point soldering iron to the pad and lead and the tinning sucked straight up from the pad to the lead. It was great. Next I'm going to see if I just place the connector on the board and reflow it, if it will connect properly.
I'm attaching a picture, it's a bit hard to see, I don't have a lens for close-ups for my DSLR. I'm pleased with the way this turned out. Next, I get to try the connector on the main board.
This is true, not much solder, but definitely a connection, so I'm pleased with the progress.
I'm not sure if it meets the guidelines - what IPC guidelines should I look at to figure that out? I found somewhere on the web that it should be a concave fillet (knew that), should be shiny (knew that), and that it shouldn't be bridging anything (knew that). But I doubt those are the technical requirements and if I remember correctly, IPC usually has different levels of acceptability - meaning quantification, something that article lacked.
Also, when I was doing the soldering work, I was trying to put a bit of solder on the end of the iron, mostly just to keep the tip tinned, but I struggled with keeping a small enough amount that it didn't glob onto the connector and create a bridge. It didn't look like it was pulling any solder off the tip but I'm not 100% sure that it didn't, either.
Thanks again for your help!
I hand solder 100 pin TQFP chips (8mil pads).
I use chip quik solder paste and chip quik flux (both from a syrnge). Prior to placing the chip I squeeze some flux on a peice of plastic then squeeze a tiny bit of solder into the flux. Mix for a bit, then apply to pads. I dont have a toaster over to reflow things (yet) so I tack each corner pin to stabilize the chip then either use reflow hot air station to melt with hot air, or use a fine tip iron to make the remaining solder connections.
Using a 5x magnifying lamp to do the work, then placing another hand magnifying glass on top of the lamp lens to check my work helps very much!
you said that you solder 100 pin TQFP chips and that you use chipquick solder paste , and chipquick flux , could you give me the part no. for those so i can order me some. I would like to try that,
I dont have the original part numbers but I just recieved my digikey order today that just so happened to have an order of paste and solder. The part numbers I ordered were... solder: SMDLTLFP , flux paste: SMD291NL.
I haven't used these specific items yet, but I'm sure they will work as good as the last stuff I bought.
Here's a tutorial on soldering and solder; well worth the price. Also on youtube are numerous rework and fine pitch soldering techniques. I've soldered over 100,000 connections and would never try to hand solder that fine pitch. If you have a stencil, your're half way to success. You need to reflow that component. Until we bought a fancy-schmancy reflow oven here at Miracle Audio, we would reflow by hand using a hot air rework tool, and there are some vids on using a standard hot air gun, but I wouldn't recommend that for this fine pitch. The most important thing you need is a great reflow solder that includes a flux. We use Cookson no-cleanAlpha SAC-305. It might not be exactly what you need but there are dozens of great tin/copper/silver alloys that qualify for RoHS. Do some research and watch some videos. The time spent learning will save you a lifetime of screw-ups. Good luck!